To assess the prevalence of different MRI patterns in patients with cerebral amyloid angiopathy (CAA) and compare their cerebrovascular risk profiles and clinical outcomes.

CAA is a major cause of intracerebral hemorrhage in elderly populations. Although characteristic MRI findings including lobar cerebral microbleeds (lCMBs) and cortical superficial siderosis (cSS) are well recognized, the relative prevalence and overlap of these phenotypic patterns remain incompletely defined.

This retrospective cohort included 377 patients diagnosed with probable CAA (Boston criteria v2.0) at a single center from 2015 to 2024. MRI scans were reviewed for lCMB, cSS, and other small-vessel disease markers. Baseline characteristics, vascular risk factors, and outcomes were compared among lCMB-only, cSS-only, and mixed groups using t-tests for continuous variables and chi-square tests for categorical data.

Among 377 patients with probable CAA, 46.1% demonstrated lCMBs only, 4.0% had isolated cSS, and 49.9% showed mixed findings. The mean age of the cohort was 76 ± 9 years and 49.6% were female. Compared with patients with lCMBs-only, those with cSS-only and mixed phenotypes showed a higher prevalence of prior ischemic stroke (40.0% and 34.0% vs 21.8%), intracerebral hemorrhage (33.3% and 42.6% vs 12.6%), and subarachnoid hemorrhage (6.7% and 16.0% vs 2.3%) (all p < 0.05). White matter hyperintensity was higher in mixed (61.7%) and lCMB-only (46.0%) than in cSS-only (33.3%) (p = 0.003), with no differences in perivascular spaces or lacunes. Compared with patients with lCMBs-only, those with cSS-only and mixed phenotypes also showed higher rates of interval ICH (27.7% and 29.8% vs 6.3%), interval stroke (46.7% and 29.3% vs 19.5%), and mortality (46.7% and 17.6% vs 16.1%) (all p < 0.05).

Although cSS was uncommon, its presence alone or in combination with lCMB was associated with poor clinical outcome (ICH, stroke, death), suggesting that cSS reflects more advanced disease and poorer prognosis in CAA.